The present invention relates to a cathode ray tube, and in particular to a cathode ray tube having reliability enhanced by improving welding accuracy of an electrode fabricated by stacking and welding together a plurality of electrode members in an electron gun housed in its vacuum envelope.
Color cathode ray tubes such as a color picture tube and a display tube, which are typical cathode ray tubes, are widely used for reception of TV broadcast and monitors of various kinds of information processing equipment because of their high-definition image reproduction capability.
Color cathode ray tubes of such a kind have a vacuum envelope comprised of a panel, a neck and a funnel for connecting the panel and the neck, a phosphor screen formed on an inner surface of the panel, and an electron gun housed in the neck for projecting an electron beam toward the phosphor screen. Especially, widely used are color cathode ray tubes employing an in-line type electron for projecting a plurality of electron beams parallel with each other in a horizontal plane.
FIG. 10 is a side view of an essential part of an embodiment of a configuration of an in-line type electron gun used for a color cathode ray tube, viewed in a direction perpendicular to a direction of the in-line arrangement of electron beams. In FIG. 10, reference numeral 31 denotes cathodes, 32 is a first electrode serving as a control electrode, 33 is a second electrode serving as an accelerating electrode, and the cathodes 31, the first electrode 32 and the second electrode 33 form an electron beam generating section.
Reference numeral 34 denotes a third electrode, and 35 is a fourth electrode. In this example, the fourth electrode 35 are formed of two tube-like electrodes 35a and 35b, and they serve as two focus electrodes. Reference numeral 36 denotes a fifth electrode, and the fifth electrode 36 and the tube-like electrode 35b of the fourth electrode 35 which forms a main lens therebetween. Reference numeral 37 denotes a shield cup, which is welded to the fifth electrode 36. The cathodes 31 and the first to fifth electrodes 32-36 are spaced with predetermined spacings and fixed in the predetermined order by a pair of insulator support rods (multiform glasses) 38. Reference numeral 39 denotes a stem, and the cathodes and the electrodes are supplied with display signals or operating voltages via stem pins 40 sealed through the stem 39.
Three electron beams are generated by the electron beam generating section which is a triode section comprised of the cathodes 31, the first electrode 32 and the second electrode 33, and are accelerated and focused by the third electrode 34, the fourth electrode 35 and the fifth electrode 36 such that the three electron beams are subjected to a desired focusing action by the main lens formed between opposing end faces of the fifth electrode 36 and the electrode 35b of the fourth electrode 35 and then directed toward the phosphor screen.
In this type of an electron gun, the first electrode 32 and the second electrode 33 are plate-like electrodes, and the third electrode 34 and the fourth electrode 35 are compound electrodes fabricated by stacking and welding together plural electrode members including a cup-shaped electrode member and a plate-like member.
FIGS. 11A1, 11A2, 11B1, 11B2, 11C1 and 11C2 are plan views and side views of electrode members forming the compound electrode shown in FIG. 10. FIGS. 11A1 and 11A2 are plan and side views of a first electrode member 1, respectively, FIGS. 11B1 and 11B2 are plan and side views of a second electrode member 2, respectively, and FIGS. 11C1 and 11C2 are plan and side views of a third electrode member 3, respectively. The first electrode member 1 and the third electrode member 3 are attached and welded by laser to the top and bottom surfaces of the second electrode member 2, respectively.
The first electrode member 1 and the third electrode member 3 are cup-shaped electrode members having rims 1b and 3b, respectively, and are formed by a drawing press. The second electrode member 2 are a plate electrode thicker than the first electrode member 1 and the third electrode member 3.
The first electrode member 1 is formed with a single opening (an electron beam-transmissive opening) 1a in a bottom at an end of its cup shape and the rim 1b at the other end of the cup shape. The rim 1b is formed with a protrusion 1c in a corner thereof for rotational alignment of the first electrode member 1 in an assembly or welding an electrical lead thereto for applying a voltage to the first electrode member 1. Similarly, the third electrode member 3 is formed with a single opening (an electron beam-transmissive opening) 3a in a bottom at an end of its cup shape and the rim 3b at the other end of the cup shape. The rim 3b is formed with a protrusion 3c in a corner thereof for indicating a position of the third electrode member 3 in an assembly or welding an electrical lead thereto for applying a voltage to the third electrode member 3.
The second electrode member 2 is formed with three electron beam-transmissive apertures 2a in its central portion on its major axis. The second electrode member 2 is fabricated by a simple punching which pierces the three apertures in a thick metal plate simultaneously with blanking, or trimming. An edge 2b is used for welding and is provided with tabs 2c approximately at centers at the respective long sides of the second electrode member 2 for being embedded into the insulator support rods (multiform glasses) 38 and thereby being fixed.
FIGS. 12A, 12B and 12C are illustrations for explaining a structure of a compound electrode integrally assembled and its welded condition, FIG. 8A is a plan view of the compound electrode, FIG. 12B is a cross-sectional view of the whole structure of the compound electrode of FIG. 12A taken along line VIIIBxe2x80x94VIIIB of FIG. 12A, and FIG. 12C is an enlarged cross-sectional view of an essential part of a welded portion in a cross section of the compound electrode of FIG. 12A taken along line VIIICxe2x80x94VIIIC of FIG. 12A. In FIG. 12A, two positions corresponding to a pair of insulator support rods (multiform glasses) 38 are indicated by two-dot chain lines.
The first electrode member 1 and the third electrode member 3 are attached to the top and bottom surfaces of the second electrode member 2, respectively, such that the edge of the rim 1b of the first electrode member 1 and the edge of the rim 3b of the third electrode member 3 are aligned with the edge 2b of the second electrode member 2, and then they are welded together by irradiating a laser beam onto the edges of the interface between the adjacent electrode members. In FIGS. 12A and 12C, the weld points are denoted by xe2x80x9cWxe2x86x92xe2x80x9d.
As shown in FIGS. 12A and 12B, the first, second and third electrodes 1, 2, 3 are attached together, and then, as shown in FIG. 12C, they are welded together by irradiating a laser beam L horizontally onto the edges of the interface between the mutually adjacent electrode members. The laser welding in this case employs a multiple-beam multiple-spot welding method capable of welding two or more spots simultaneously. In FIG. 12C, the weld points are denoted by circles xe2x80x9c∘xe2x80x9d.
The above-explained compound electrodes are not limited to one comprised of three electrode members as explained above, but are applicable to one comprised of a plate-like electrode member and a cup-shaped electrode member stacked and welded on the plate-like electrode member.
But, as shown in FIG. 12D, when the second electrode member 2 is punched out by use of a die 50 and a punch 51, sloping surfaces 53 are produced at forward edges of the second electrode member 2 in a direction of travel of the punch 51 because its material flows into the die 50, and these sloping surfaces 53 are generally called xe2x80x9cshear droop.xe2x80x9d Consequently, as shown in FIG. 12C, a gap occurs between the edge of the first electrode member 1 and the shear droop 53 of the second electrode member 2 welded to the first electrode member 1. A similar phenomenon also occurs when a thin material is used, but the above phenomenon is pronounced when a thick material is used.
Welding of the stacked. electrode members is performed by irradiating a laser beam L horizontally onto the interface of the stacked edges of the electrode members, as shown in FIG. 12C.
The laser welding in this case employs a multiple-beam multiple-spot welding method capable of welding two or more spots simultaneously. In FIG. 12C, two laser beams L perform welding of the first and second electrode members 1, 2 and welding of the second and third electrode members 2, 3, respectively, at the same time. Reference numeral 100 denote lenses.
Both of the two laser beams L having the same focal length are focused onto the edges of the stacked electrode members, and this means that, in the case of welding an edge of the second electrode member 2 having the shear droop, the laser beam L is focused onto the interface between the edge of the first electrode member 1 and a point of the edge of the second electrode member 2 where the shear droop begins, as shown in FIG. 12C. Therefore, a weld point of the first and second electrode members 1, 2 is displaced from a focal point of the laser beam by a distance D (Dxe2x89xa00). Consequently, the energy of the laser beam becomes weak in the innermost of the shear droop, resulting in so-called weak welding. The welding strength in the innermost of the shear droop is poor such that a compound electrode is not sufficiently integrally assembled, thereby sufficient assembling accuracy is not achieved, and further it is difficult to attain long lifetime of a cathode ray tube because of variations of performance characteristics due to aging.
To prevent occurrence of such weak welding, the power of the laser beam L has been sometimes increased. In this case, there is a problem in that, in FIG. 12C, the energy of the laser beam irradiated to the weld point of the second and third electrode members 2, 3 becomes excessive, and consequently, it causes loss in material of the third electrode member 3 made of a thin material due to melting and unwanted distortion and they cause deformation in the third electrode member 3 during subsequent heat treatment and deteriorate reliability.
It is an object of the present invention to provide a cathode ray tube incorporating an electron gun employing a high-precision and highly reliable electrode capable of preventing occurrence of the weak welding by solving the above-explained problem with the prior art.
To accomplish the above objects, in accordance with an embodiment of the present invention, there is provided a cathode ray tube comprising an evacuated envelope including a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a phosphor screen formed on an inner surface of the panel portion, and an electron gun housed in the neck portion; the electron gun comprising an electron beam generating section having a cathode, an electron beam control electrode and an accelerating electrode arranged in the order named for projecting an electron beam toward the phosphor screen, and an electron beam focusing section for focusing the electron beam from the electron beam generating section onto the phosphor screen, the electron beam generating section and the electron beam focusing section being mounted in predetermined spaced relationship on a plurality of insulator support rods, the electron beam focusing section including at least one compound electrode comprising a first electrode member, a second electrode member and a plate-like electrode member sandwiched therebetween, the plate-like electrode member being fabricated from a material thicker than materials from which the first electrode member and the second electrode member are fabricated, the plate-like electrode member being laser-welded to the first and second electrode members at points of edges of the first and second electrode members, the points of edges of the first and second electrode members being positioned so as not to face mounting tabs of the plate-like electrode member embedded in the plurality of insulator support rods, and edges of the plate-like electrode member extending by an approximately equal distance outwardly beyond the points of edges of the first and second electrode members welded to the plate-like electrode member.
To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a cathode ray tube comprising an evacuated envelope including a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a phosphor screen formed on an inner surface of the panel portion, and an electron gun housed in the neck portion; the electron gun comprising an electron beam generating section having a cathode, an electron beam control electrode and an accelerating electrode arranged in the order named for projecting an electron beam toward the phosphor screen, and an electron beam focusing section for focusing the electron beam from the electron beam generating section onto the phosphor screen, the electron beam generating section and the electron beam focusing section being mounted in predetermined spaced relationship on a plurality of insulator support rods, the electron beam focusing section including at least one compound electrode comprising a first cup-shaped electrode member having a flange at an open end thereof, a second cup-shaped electrode member having a flange at an open end thereof and a plate-like electrode member sandwiched therebetween, the plate-like electrode member being fabricated from a material thicker than materials from which the first cup-shaped electrode member and the second cup-shaped electrode member are fabricated, the plate-like electrode member being laser-welded to the first and second cup-shaped electrode members at points of edges of the flanges of the first and second cup-shaped electrode members, the points of edges of the flanges of the first and second cup-shaped electrode members being positioned so as not to face mounting tabs of the plate-like electrode member embedded in the plurality of insulator support rods, and edges of the plate-like electrode member extending by an approximately equal distance outwardly beyond the points of edges of the flanges of the first and second cup-shaped electrode members welded to the plate-like electrode member.
To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a cathode ray tube comprising an evacuated envelope including a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a phosphor screen formed on an inner surface of the panel portion, and an electron gun housed in the neck portion; the electron gun comprising an electron beam generating section having a cathode, an electron beam control electrode and an accelerating electrode arranged in the order named for projecting an electron beam toward the phosphor screen, and an electron beam focusing section for focusing the electron beam from the electron beam generating section onto the phosphor screen, the electron beam generating section and the electron beam focusing section being mounted in predetermined spaced relationship on a plurality of insulator support rods, the electron beam focusing section including a focus electrode, a compound electrode and an anode supplied with a highest voltage, arranged in the order named toward the phosphor screen, the compound electrode supplied with an intermediate voltage between the highest voltage and a voltage supplied to the focus electrode, the intermediate voltage being obtained by dividing the highest voltage via a resistor housed in the cathode ray tube, the compound electrode comprising a first cup-shaped electrode member having a flange at an open end thereof, a second cup-shaped electrode member having a flange at an open end thereof and a plate-like electrode member sandwiched therebetween, the plate-like electrode member being fabricated from a material thicker than materials from which the first cup-shaped electrode member and the second cup-shaped electrode member are fabricated, the plate-like electrode member being laser-welded to the first and second cup-shaped electrode members at points of edges of the flanges of the first and second cup-shaped electrode members, the points of edges of the flanges of the first and second cup-shaped electrode member being positioned so as not to face mounting tabs of the plate-like electrode member embedded in the plurality of insulator support rods, and edges of the plate-like electrode member extending by an approximately equal distance outwardly beyond the points of edges of the flanges of the first and second cup-shaped electrode members welded to the plate-like electrode member.
To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a cathode ray tube comprising an evacuated envelope including a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a phosphor screen formed on an inner surface of the panel portion, and an electron gun housed in the neck portion; the electron gun comprising an electron beam generating section having a cathode, an electron beam control electrode and an accelerating electrode arranged in the order named for projecting an electron beam toward the phosphor screen, and an electron beam focusing section for focusing the electron beam from the electron beam generating section onto the phosphor screen, the electron beam generating section and the electron beam focusing section being mounted in predetermined spaced relationship on a plurality of insulator support rods, the electron beam focusing section including at least one compound electrode comprising a first electrode member, a second electrode member and a plate-like electrode member sandwiched therebetween, the plate-like electrode member being fabricated from a material thicker than materials from which the first electrode member and the second electrode member are fabricated, the first electrode member being stacked on a surface of the plate-like electrode member having shear droop caused in punching out the plate-like electrode member, the second electrode member being formed with cutouts at edges thereof, the plate-like electrode member being laser-welded to the second electrode member and the first electrode member at the cutouts of the second electrode member and points of edges of the first electrode member corresponding to the cutouts of the second electrode member, respectively, the cutouts of the second electrode member and the points of edges of the first electrode member being positioned so as not to face mounting tabs of the plate-like electrode member embedded in the plurality of insulator support rods.
In the punching operation, the thicker the material, the greater the shear droop. Generally in a compound electrode, a rim of a cup-shaped electrode member made of a thin material is welded to a thick plate-like electrode member. The edge of the thick plate-like electrode member is extended beyond the rim of the cup-shaped electrode member such that, even if the shear droop of the thick plate-like electrode member is somewhat superposed on the rim of the cup-shaped electrode member, a gap formed therebetween is made smaller, or if the shear droop of the thick plate-like electrode member is extended so as not to be superposed on the rim of the cup-shaped electrode member, no gap is formed between thick plate-like electrode member and the cup-shaped electrode member at a weld point of the two electrode members, and consequently, the respective laser beams are focused on intended points and realizes precision welding.
The present invention is not limited to the above configurations, but various changes and modifications may be made without departing from the nature and spirit of the present invention.